"Glenn Simpson, through his attorney, has declined to voluntarily attend Wednesday’s Judiciary Committee hearing regarding compliance with the Foreign Agents Registration Act. Therefore, a subpoena has been issued to compel his attendance. Simpson’s attorney has asserted that his client will invoke his Fifth Amendment rights in response to the subpoena," the statement said on Friday.
In 2015, Simpson's firm, Fusion GPS, hired former British intelligence agent Christopher Steele to compile opposition research on then candidate Trump.
In January, CNN and BuzzFeed media outlets reported on the dossier, which alleges that Trump was groomed and supported by Russian intelligence for several years.
On January 13, Kremlin spokesman Dmitry Peskov called the dossier a forgery. The US president also called the collection of documents fake and said it was put together by his opponents.
The Senate Judiciary Committee is probing Russia's alleged interference in the 2016 US election.
Moscow denies meddling in the vote.
Russian officials have repeatedly denied the allegations of meddling in US elections, calling them absurd and created to deflect public opinion from pressing domestic issues.
